A continuously variable belt transmission usually consists among other things of a starting unit, a forward/reverse drive unit or a reversing gearset, an intermediate shaft, a differential, hydraulic and electronic control devices, and a variator.
According to the prior art, in such transmissions the variator comprizes a primary and a secondary gearset, also called the primary and secondary side, both gearsets being formed as conical disks and are arranged in pairs. In addition, a variator is provided with a torque-transmitting belt element which runs between the two conical disk pairs. In this the current transmission ratio is defined by the running radius of the belt element, which in turn is a function of the axial position of the conical disks.
From DE 199 50 053 there is known a continuously adjustable vehicle transmission with a variator for the continuously variable adjustment of transmission ratio and with a multi-stage gearbox having at least one input shaft and one output shaft and with at least two forward gears and at least one reverse gear.
In this, in the multi-stage gearbox a rotation direction reversal takes place between the input and output shafts by virtue of the at least two forward gears, whereas the reverse gear is designed with no rotation direction reversal between the input and output shafts.
The device for reversing the rotation direction can be a spur gear stage arranged downstream from a speed transmission. In particular, the multi-stage gearbox or reversing gearset is a planetary transmission connected via a spur gear stage to a downstream axle differential for driving the wheel axles of a motor vehicle.
Continuously variable transmissions are also known, whose gear change device, which is formed as a synchronization or claw clutch, has a dual action on two pairs of gearwheels to engage various transmission ratios, the gear change device being arranged between the gearsets. This design takes up considerable structural space in the axial direction between the gearsets in order to accommodate the gear change device together with actuation devices acting from outside.
In the case when the reversing gearset comprizes a planetary gearset, it is known to construct this as a planetary gearset with double planetaries and a 1:1 transmission ratio; this gives the advantage that on starting, the same transmission ratio can be realized in both the forward and the reverse directions.
However, this design solution has the disadvantage of being elaborate to manufacture and assemble; furthermore, its production costs are high.
To avoid these disadvantages it has been proposed to construct the planetary gearset of the reversing gear as a simple planetary gearset, such that the drive input shaft is connected to the annular gear of the planetary gearset and the primary shaft to the sun gear of the planetary gearset. This, on the one hand, reduces the manufacturing complexity and costs; on the other hand, with this design the torque available in reverse gear is lower since there is a speed step-up. In certain situations this can have the disadvantageous result that not enough torque is available when starting in reverse. Besides, no compensation is possible by a corresponding adjustment of the variator.